1. Field of the Invention
The present invention relates to underwater trenching apparatuses in general. In particular, the present invention relates to an apparatus for digging an underwater trench in hard bottom bodies of water with a mechanical cutter apparatus and simultaneously laying a continuous length of pipe in the trench as cut.
2. General Background
It is a common practice in the oil and gas industry that, in order to move oil or gas from offshore on to land, often time requires laying of pipe for transport of the oil or gas. Due to requirements by the Environmental Protection Agency or other government agencies, it is required that the underwater pipe be laid in a trench dug at the bottom of the body of water with the action of the water backfilling the trench subsequent to the laying of the pipe. In the present state of the art, most underwater trenching which is done in the softer bottom areas of the gulf and other bodies of water, is accomplished with the use of a underwater trenching apparatus utilizing a "jet sled" with highly compressed air or water being used as the trenching device, with the compressed air or water literally digging a trench in the hard or soft silt bottom which is then inlaid with a continuous row of pipe or the like.
However, often times in the laying of pipe, one comes across an area of the gulf or the body of water which has a very substantially solid bottom, such as shale or the like, which cannot be cut out with the use of a jet sled and the highly compressed air or water, due to the substantial layer of hard bottom. Therefore, a device must be utilized which mechanically cuts out the trench, with the use of augers or the like, in order to assure that the trench is cut for the laying of the pipe.
Several inventions have been patented which speak towards the mechanical device for trenching out a trench for laying of cables or pipe underwater. The most pertinent are as follows:
U.S. Pat. No. 3,925,532 issued to Spearman entitled "Underwater Trenching and Cable Laying Apparatus" would teach the use of a sled which supports a hydraulic motor drive digging wheel for cutting out a trench and feeding conduit in the trench for laying of conduit beneath the water. The apparatus utilizes a rotary digging wheel which would cut substantially a width of a trench necessary to lay a cable or the like, and does not address the problem of digging a substantially broad trench for the laying of pipe as in our particular apparatus.
U.S. Pat. No. 3,852,972 issued to Holberg entitled "Submerged Pipeline Burial Apparatus" would teach the use of a pipeline burial apparatus having a support structure carried along the pipeline by a movable carriage and includes a plurality of inclinded augers for cutting or digging beneath the pipe to which the pipe is to be laid. In this particular invention, the cutting means is the plurality of augers which are angulated down into the earth for cutting the trench wherein the pipe is to be laid.
U.S. Pat. No. 3,978,679 issued to Lecomte entitled "Method and Apparatus for Underwater Trench Excavation and Pipeline Laying" would teach the use of an apparatus for excavating a trench with the use of an excavation machine which moves alongside the pipeline and digs out material from beneath the pipeline. The patent discloses the cutting means as a rotary type of cutter at the end of an articulated arm for trenching out the area directly beneath the pipe as the pipe is set on the bottom of the body of water.
U.S. Pat. No. 3,238,734 issued to R. F. Rhodes entitled "Apparatus for Burying and Recovering Pipe in Underwater Locations" would teach the use of an apparatus having a pair of cuttings means set upon a chain or the like for excavating an area which would substantially house a pipe therewithin after the area has been excavated by the pair of trenching apparatuses. The apparatuses would have the ability to be angulated in towards one another for digging out a trench or the like for laying of the pipe therewithin.
Other patents which teach the use of trenching apparatuses are U.S. Pat. No. 3,412,490 issued to F. M. Reising entitled "Trenching Machine"; U.S. Pat.No. 737,021 issued to B. Roberts entitled "Submarine Cable Laying Device"; and U.S. Pat. 4,245,927 issued to Wharton entitled "Laying of Pipes or Cables in a Bed of Material".